This invention relates to a novel aromatic sulfonic acid derivative dopant which is applicable to a conductive polymer material; a conductive polymer material containing the dopant; and a solid electrolytic capacitor using the polymer material. In particular, this invention relates to a conductive polymer material with good heat resistance and moisture resistance which is suitable for manufacturing a solid electrolytic capacitor, and a solid electrolytic capacitor in which the polymer material is used as a cathode conductive material.
In recent years with the advance in electronics technology, novel electronic materials have been developed. In particular, remarkable technological innovation has been achieved in the area involving high performance organic materials. Even if the scope of view is restricted to the conductive materials alone, there have been developed conductive polymer materials produced by way of doping electron-conjugated polymers such as polyacetylene, polyparaphenylene, polypyrrole, and polyaniline with some electron acceptable compounds as the dopant. And, there are even cases in which newly developed materials have been actually industrialized as a capacitor electrode material, a battery electrode material and an antistatic material.
However, for extending industrial applicability of these conductive polymer materials, significant problems involving environmental stability such as heat resistance and moisture resistance must be solved, besides further improvement in conductivity.
For solving these problems encountered in industrialization, we have provided, in terms of environmental stability, a xcfx80-electron conjugated polymer material comprising an m-sulfobenzamide derivative as a dopant, exhibiting both higher conductivity and improved heat resistance in Japanese Laid-open Patent Publication 2000-204074.
For example, we have found that polypyrrole doped with m-sulfobenzamide exhibits considerably slow reduction in a conductivity even when being placed in the air at 150xc2x0 C. and can maintain a high conductivity of 100 S/cm or more.
Polypyrrole doped with m-sulfobenzamide, however, rapidly loses its conductivity when the atmosphere contains moisture at a high temperature. Thus, for extending industrial applicability of a conductive polymer material, it is essential that the material exhibits improved stability under the moisture-containing atmosphere at a high temperature, i. e., under the conditions of a high temperature and a high humidity.
Thus, an objective of this invention is to provide a dopant which endows a xcfx80-electron conjugated polymer material with a higher conductivity which can be retained even under the environmental conditions of a high temperature and a high humidity; a conductive polymer material with good heat resistance and good moisture resistance; and a solid electrolytic capacitor comprising the polymer material.
Namely, this invention relates to a dopant comprising at least one of aromatic sulfonic acid derivatives represented by general formulas 1 and 2; a conductive polymer material containing the dopant which exhibits good heat resistance and good moisture resistance; and a solid electrolytic capacitor comprising the polymer material. 
wherein at least one of R1 to R6 represents a sulfonic acid group having a counter cation selected from the group consisting of a hydrogen ion, an alkali metal ion, an alkaline-earth ion and a transition metal ion belonging to groups 8 to 10 in the periodic table; and the remaining R1 to R6, which may be the same or different, represent hydrogen, alkyl having four or less carbon atoms or phenyl; or any two or more of R1 to R6 may be combined together to form an aromatic or aliphatic ring. 
wherein at least one of R7 to R10 represents a sulfonic acid group having a counter cation selected from the group consisting of a hydrogen ion, an alkali metal ion, an alkaline-earth ion and a transition metal ion belonging to groups 8 to 10 in the periodic table; and the remaining R7 to R12, which may be the same or different, represent hydrogen, alkyl having four or less carbon atoms or phenyl; or any two or more of R7 to R10 may be combined together to form an aromatic or aliphatic ring.